Machine for manufacturing steel structural parts

ABSTRACT

Disclosed is an electric welding machine including an endless chain of welding heads, each head supporting opposite electrode holders for longitudinal rods and grippers for transverse rods, and cam means operable for controlling the operative and inoperative positions of the holders and grippers.

United States Patent 1151 3,699,756 Ritter et al, 1 Oct. 24, 1972 [54]MACHINE FOR MANUFACTURING STEEL STRUCTURAL PARTS Inventors: KlausRitter; Hans Gott; Josef Ritter; Gerhard Ritter, all of Graz, AustriaAssignee: EVG Entwicklungs-und Verwertungsgesellschaft mbH, Graz,Austria Filed: Nov. 29, 1971 Appl. No.: 202,935

Foreign Application Priority Data Austria ..A 10732/70 Nov. 27, 19701111.01. ..B23k 11/02 Field of Search....2l9/l03, 56,57, 58, 106, 107,219/104, 78, 79, 80, 86, 87, 83

[56] References Cited UNITED STATES PATENTS 3,056,883 lO/l962Eisenburger et a1. ....2l9/56 X 3,612,816 10/1971 Hand ..219/87 X1,271,428 7/1918 Burns ..219/78 Primary Examiner-J. V. Truhe AssistantExaminer-B. A. Reynolds Attorney-Emest F. Marmorek [57] ABSTRACTDisclosed is an electric welding machine including an endless chain ofwelding heads, each head supporting opposite electrode holders forlongitudinal rods and grippers for transverse rods, and cam meansoperable for controlling the operative and inoperative positions of theholders and grippers.

5 Claims, 7 Drawing Figures PATENTEDUBT 2 m2 3.699.156

SHEET 2 [IF 4 MACHINE FOR MANUFACTURING STEEL STRUCTURAL PARTS Theinvention relates to the manufacture of steel structural parts,consisting of two parallel longitudinal rods connected together bywelded transverse rods. Special structural parts of this kind are thesubject of our US. Pat. No. 728,866 and are on the market under thetrade name Bi-Steel for use as reinforcement for concrete.

The method usually employed for manufacturing steel structural parts ofthis kind is as follows. The two longitudinal rods are fed into thewelding machine convergently so that their distance apart at the weldinglocation is a little greater than the distance apart desired in thefinished product. A cut off length of transverse rod is fed intoposition between the longitudinal rods, at the welding location,clearances remaining between the ends of the transverse rod and the twolongitudinal rods, whereupon the two longitudinal rods are thrusttowards each other by external electrodes, which thrust them firmly intocontact with the ends of the transverse rod, applying the necessarywelding pressure. Finally the longitudinal rods are welded to thetransverse rod, preferably by sequential spot welding, after which thestructure is advanced one step, ready for the next welding operation. Itwill be observed that the longitudinal rods are advanced intermittently,the welding taking place during the intervals when they are stationary.

In order to increase the output of a machine for manufacturingstructural parts of this kind, the present applicant has previouslyproposed to arrange the machine in such a way that the longitudinal andtransverse rods are advanced continuously. The welding is done by thesequential spot welding method. Two electrodes circulating on closedpaths thrust inwards from either side against the outer surfaces of thelongitudinal rods, thrusting them firmly against the ends of thetransverserod, so as to retain the transverse rod in position and applythe necessary welding pressure. The external electrodes, thelongitudinal rods and the transverse rod all travel along togetherduring the welding operation.

The fact that the electrodes travel along with the continuouslyadvancing rods has two advantages. In the first place this ensures thatthe welding current is applied long'enough to ensure that a good weld ismade. Secondly the method ensures that the welding current heats therods only in the immediate neighborhood of the welding location. This isimportant in the manufacture of Bi-Steel, because the longitudinal rodsare cold drawn steel rods with comparatively high concentrations ofalloying elements, particularly carbon. The welding heat must thereforebe applied as nearly as possible only at the welding location, toprevent modification of the metallurgical properties of these steels.

In accordance with the invention, in a machine for manufacturing steelstructural parts consisting of two parallel longitudinal rods connectedtogether by welded transverse rods, the machine comprises means forfeeding the two longitudinal rods convergently, means for introducingthe transverse thrust rods between the longitudinal rods and electricresistance welding heads for welding the transverse rods to thelongitudinal rods; several welding heads are linked together to form anendless chain which is driven continuously so that the chain follows aclosed path in the plane of symmetry between the two longitudinal rods,the path of the chain having a straight welding stretch extendingparallel to the plane of the two longitudinal rods, each welding headhaving a gripper for receiving and holding in position a transverse rodand two welding electrodes one on each side of the gripper, the twowelding electrodes being arranged to move towards and away from eachother, thrust devices being provided for moving the welding headstowards each other and for applying the necessary welding pressure, afeeding device being provided, on the chain path, for feeding transverserods to the grippers, and there being means for conducting electriccurrent to the welding electrodes.

The present invention thus provides an improved machine which isarranged in such a way that during the welding process each transverserod is retained reliably and precisely in the correct position relativeto the longitudinal rods. The new machine further ensures that thewelding thrust applied by each electrode, which partly determines thequality of the weld, is applied precisely perpendicular to the axis ofthe longitudinal rod at the welding location and in line with the axisof the transverse rod, so that the welding pressure is distributedsymmetrically over the cross section of the transverse rod. This is toensure that when the steel rod structure is installed in concrete andtension is applied to the longitudinal rods, so that a bending stressacts on the transverse rod, which anchors the rod structure in theconcrete, the strength of the weld is independent of the direction ofthe tensile stress applied to the longitudinal rods.

A machine constructed in accordance with the invention is illustrated inthe accompanying drawings, in which:

FIG. 1 is a diagrammatical side view showing the circulating weldinghead chain of a device according to the invention and showing also thefeeding devices for feeding the longitudinal and transverse rods;

FIG. 2 is a plan view corresponding to FIG. 1 but drawn to a somewhatlarger scale, showing the arrangements for actuating the weldingelectrodes and indicating also arrangements for feeding electric weldingcurrent;

FIG. 3 is a partly sectioned side view of the welding head chain,showing one welding head sectioned noncentrally and two welding headswhich are shown sectioned centrally;

FIG. 4 is a diagrammatic side view of a feeding device for feedingtransverse rods;

FIG. 5 is a corresponding cross section; and

FIGS. 6 and 7 represent diagrammatically a different feedingarrangement.

As shown in FIGS. 1 and 2, a number, for example 16, of welding heads 1are linked together by pivot pins to form a chain 3 of welding heads,somewhat similar to a bicycle chain. The chain of welding headscirculates endlessly over two terminal sprocket wheels 4 and 5, at leastone of which is continuously power driven, so that the welding headscirculate continuously. The sprocket wheels 4 and 5 are merely indicatedin the drawing. Each sprocket wheel is in the form of one or morecircular or square discs, with notched edges for accommodating the pivotpins 2, or bushes or the like mounted on the pivot pins.

The upper strand of the chain follows a straight path, that is to saythe welding heads 1 move along in a straight path, as represented inFIG. 1, the welding heads moving along at the height of the plane Vcontaining the longitudinal wires L1, L2, which are being fedconvergently, guided by rollers 6a, 6b. In FIG. 2 the vertical plane ofsymmetry between the two longitudinal wires L1 and L2 is indicated at S.This is also the middle line of the path followed by the welding heads.

As shown in the non-central section 1a in FIG. 3, each welding head hasa base part 7 from which project arms 8, joined by pivot pins 2 to thearms of the neighboring welding heads in the chain. The upper surface ofthe base part 7 is arranged as a guide, for example the dovetail guide 9shown in FIG. 3, along which two electrode holders 10 and 10 (compareFIG. 2) can slide towards and away from each other. Each electrodeholder 10, 10' supports an electrode 11, 11'.

In the middle of each base part 7 there is an opening 12, as shown inthe centrally sectioned welding heads lb and 1c in FIG. 3. One arm of anangled lever in the form of a pivoted jaw 13 projects upwards throughthe opening 12. The pivoted jaw 13 is pivoted on the forward pivot pin 2of the welding head. Mounted; on the pivoted jaw 13 at its elbow thereis a cam follower roller 14, which follows a cam surface 19. The pivotedjaw 13 cooperates with a spring loaded sliding jaw 17, which is loadedby a spring 18 which tends to hold the sliding jaw 17 in the positionshown at 1c in FIG. 3. In this position the movement of the sliding jaw17 is limited by stops 7a and 17a.

The cam surface 19 is the surface of a cam rail extending all along thepath followed by the welding head chain. The cam follower roller 14 ofeach welding head 1 follows the cam rail 19. The curve of the cam rail19 is arranged so that at a certain location along the cam rail thepivoted jaw 13 closes against the spring loaded sliding jaw 17, grippinga transverse rod Q, which has previously been fed into a positioningnotch 20. The transverse rod Q is shown gripped in position at 1b inFIG. 3. The transverse rod Q remains gripped, that is to say it isretained in the positioning notch 20 by the two gripping jaws during theperiod required for welding the ends of the transverse rod to the twolongitudinal rods L1 and L2. The feeding of the transverse rod'Q intothe positioning notch 20 will be described further below. The transverserod can be fed into the positioning notch 20 at any suitable location onthe path of movement of the welding head chain. The transverse rod ishowever preferably fed to the lower strand of the circulation weldinghead chain, that is to say the transverse rod is fed into thepositioning notch 20 when the welding head is upside down, thetransverse rod being fed into the positioning notch 20 from underneath.The positioning notch 20 ensures that the transverse rod Q is heldprecisely in position while it is being welded to the longitudinal rodsL1 and L2.

At their outer ends the two electrode holders 10, 10' of each weldinghead 1 have forks in which rotate thrust rollers 24, 24', as shown inFIG. 2. When the rollers 24, 24 are not in contact with cam rails 28 and28' the two electrode holders 10, 10', with their electrodes 11, 11' arethrust apart, against mechanical stops, by springs which are not shownin the drawing, so that the two electrodes 11 and 11 are as far apart asthey can When the electrode head 1 is travelling along the path of theupper strand of the welding head chain the two electrode holders 10, 10'are thrust inwards, towards each other, by the two cam rails 28, 28', sothat the two electrodes 11, 11 are thrust inwards against the outersurfaces of the two longitudinal rods L1, L2, the cam rails 28, 28thrusting against the rollers 24, 24'. The thrust of the electrodesagainst the longitudinal rods is sustained all through the weldingperiod to ensure that good welds are made. It should be observed thatthe welding thrusts are applied entirely symmetrically due to thestraight line movements of the electrode holders, the arrangementproviding the best possible welding conditions.

The welding current can be fed to the electrodes in I various ways, andcan be switched on and off by various methods. In FIG. 2 it has beenassumed, as an example, that at least one of the two electrode holders10, 10' is electrically insulated against the base part 7 of the weldinghead 1, the welding current being fed to the welding electrode 11 overthe thrust roller 24, which acts as a contact roller. In this case thecam rail 28 can be constructed of an electrically insulating material,the cam rail 28 being however equipped with a conductor bar 30 to whichthe welding current is fed from a welding transformer, as indicated bythe plus sign in FIG. 2. The other cam rail 28' can be made of anelectrically conductive material and can be connected to the other,earthed pole of the welding transformer. The welding current circuit isclosed during the period taken by the welding head to travel over thedistance D shown in FIG. 2. At a location;further downstream along thepath of movement there can be a further contact bar 31 on the cam rail28, this contact bar 31 being at a different voltage relative to the camrail 28'. The arrangement allows the welding to be followed by a heattreatment to improve the metallurgical quality of the welded metal. Theelectric contacts can if desired be arranged so that welding current issupplied to only one welding head at a time, or to several welding headsconnected in parallel or fed with different phases from a polyphasesupply, moreover the duration of the current supply can if desired bycontrolled in the known way by external switches.

FIGS. 4 and 5 show an example of a feeding device for feeding transverserods to the welding heads 1 moving along the lower strand of the weldinghead chain. Of the welding head itself FIG. 4 shows only the lower endof the pivoted jaw 13 and of the spring loaded sliding jaw 17, showingthese two jaws closed for holding the transverse rod Q. Anintermittently rotating wheel 44 has three receiver notches 32a, 32b,32c, spaced equally apart at for receiving the transverse rods Q. InFIG. 4 the notched wheel 44 is represented in a position which itoccupies during one of its intermittent rotations. When the notchedwheel 44 is in its position of rest, one of the notches, for example thenotch 32a,

is in the position I. When the notch is in this position a cut offlength of transverse rod Q is fed into the notch from the side by thefeeder tube 35 shown in FIG. 5. The cut off length of transverse rod Qis fed into the positioning notch 20 of the welding head as follows. Thenotched wheel 44 rotates through 240, bringing the notch 320 into theposition III. During this rotation the transverse rod is fed into thepositioning notch 20 of the welding head, which is constantly travellingpast the feeding device. In FIG. 4 a cut off length of transverse rod Qis shown in a notch 32c of the notched wheel 44, the transverse rodbeing shown during the process of transfer into the positioning notch 20of the welding head. The feeding device has slotted cheek plates 33, oneon each side of the notched wheel 44. Each cheek plate has anessentially semi-circular guiding channel 34 with a sloping edge 34a fordelivering the transverse rod into the positioning notch 20 of thewelding head. The sloping edges 34a bear against the ends of thetransverse rod. Assuming that the notched wheel 44 is initially in itsposition of rest, the transverse rod in the notch 32a being at theposition I, the notched wheel 44 begins rotating, accelerating until thetransverse rod, its ends guided by the semi-circular slot, is fed intothe positioning notch 20 of the welding head, the periphery of thenotched wheel 44 travelling at this instant at the same linear speed asthe welding head. The transverse rod is fed into the positioning notch20 by the sloping slot edges 34a, which bear against the ends of thetransverse rod. Finally the notched wheel 44 deccelerates, bringing thenotch 32a to rest in the position III, the notch 32b being now in theloading position I, whereupon the cycle is repeated.

FIG. 1 shows three feeding devices of the kind shown in FIGS. 4 and 5,the three feeding devices being positioned-one after the other so thatthree welding heads can be fed simultaneously with transverse rods Q.Subsequently the three welding heads, after reaching the upper strand Tof the welding head chain, can be energized with the three phases of a3-phase current supply. This arrangement increases the output of themachine.

FIGS. 6 and 7 correspond to FIGS. 4 and 5 but show a feeding device ofdifferent construction, in which instead of an intermittently rotatingfeeder wheel there is a reciprocating feeder device. A reciprocating rod41 drives a reciprocating comb 42 which has three receiver notches 42a,42b, 420 for receiving the transverse rods and delivering them to thewelding heads. Cut off lengths of transverse rod Q can be fed from theside through a loading tube 35 into the receiver notches of the comb 42.The comb 42 slides back and forth in a guide 43 of U-shaped crosssection which has sloping edges 43a, 43b, 430 which bear against theends of the transverse rods Q. For feeding the transverse rods into thepositioning notches of the welding heads, the comb 42 is accelerated bythe rod 41 up to the linear velocity of the welding heads 1, asindicated by the arrow. The ends of the transverse rods run up over thesloping surfaces 43a, 43b, 43c, which thrust them upwards between thejaws of three passing welding heads.

The examples of the invention represented can be modified in a number ofways. The travelling movements of the electrodes, their inwardsmovements and the movements of the gripping jaws which hold thetransverse rods precisely in position can be produced by other distancedependent mechanical devices, other than cam rails cooperating withthrust rollers. The

feeding devices, for feeding the transverse rods, can be constructeddifferently and they can be installed at other locations. If desired thegrippers for gripping the transverse rollers can be equipped withpermanent magnets or electromagnets.

We claim;

l. A machine for manufacturing steel structural parts consisting of twoparallel longitudinal rods connected together by welded transverse rods,the machine comprising means for feeding the two longitudinal rodsconvergently, means for introducing the transverse thrust rods betweenthe longitudinal rods and electric resistance welding heads for weldingthe transverse rods to the longitudinal rods, wherein several weldingheads are linked together to form an endless chain which is drivencontinuously so that the chain follows a closed path in the plane ofsymmetry between the two longitudinal rods, the path of the chain havinga straight welding stretch extending parallel to the plane of the twolongitudinal rods, each welding head having a gripper for receiving andholding in position a transverse rod and two welding electrodes one oneach side of the gripper, the two welding electrodes being arranged tomove towards andaway from each other, thrust devices being provided formoving the welding heads towards each other and for applying thenecessary welding pressures, a feeding device being provided, on thechain path, for feeding transverse rods to the grippers, and there beingmeans for conducting electric current to the welding electrodes.

2. A machine according to claim 1, in which each welding head has a basepart equipped with parallel guides extending perpendicular to the lengthof the welding head chain, the guides guiding two electrode holders,electric conductors being provided on either side of the weldingstretch, for example in the form of cam rails which act on thrustrollers mounted on the electrode holders for advancing the weldingelectrodes into contact with the longitudinal rods, and for applying thewelding thrusts.

3. A machine according to claim 2, in which each welding head isequipped, between its two electrode holders, with a gripper having jawsoperable for gripping a transverse rod, one of said jaws being providedwith a cam follower and additional cam rails extending along the path ofthe welding head chain in contact with said cam follower controlling theclosing and opening of the jaws of the gripper.

4. A machine according to any one of claims 1 to 3, in which two or moreintermittent transverse wire loaders are provided, together capable ofsimultaneously loading transverse wires to the same number of weldingheads, the loaded welding heads subsequently all receiving weldingcurrent simultaneously.

5. A machine according to claim 4, in which there are three wire loadersand the three loaded welding heads each receive one phase from a 3-phasecurrent source.

1. A machine for manufacturing steel structural parts consisting of twoparallel longitudinal rods connected together by welded transverse rods,the machine comprising means for feeding the two longitudinal rodsconvergently, means for introducing the transverse thrust rods betweenthe longitudinal rods and electric resistance welding heads for weldingthe transverse rods to the longitudinal rods, wherein several weldingheads are linked together to form an endless chain which is drivencontinuously so that the chain follows a closed path in the plane ofsymmetry between the two longitudinal rods, the path of the chain havinga straight welding stretch extending parallel to the plane of the twolongitudinal rods, each welding head having a gripper for receiving andholding in position a transverse rod and two welding electrodes one oneach side of the gripper, the two welding electrodes being arranged tomove towards and away from each other, thrust devices being provided formoving the welding heads towards each other and for applying thenecessary welding pressures, a feeding device being provided, on thechain path, for feeding transverse rods to the grippers, and there beingmeans for conducting electric current to the welding electrodes.
 2. Amachine according to claim 1, in which each welding head has a base partequipped with parallel guides extending perpendicular to the length ofthe welding head chain, the guides guiding two electrode holders,electric conductors being provided on either side of the weldingstretch, for example in the form of cam rails which act on thrustrollerS mounted on the electrode holders for advancing the weldingelectrodes into contact with the longitudinal rods, and for applying thewelding thrusts.
 3. A machine according to claim 2, in which eachwelding head is equipped, between its two electrode holders, with agripper having jaws operable for gripping a transverse rod, one of saidjaws being provided with a cam follower and additional cam railsextending along the path of the welding head chain in contact with saidcam follower controlling the closing and opening of the jaws of thegripper.
 4. A machine according to any one of claims 1 to 3, in whichtwo or more intermittent transverse wire loaders are provided, togethercapable of simultaneously loading transverse wires to the same number ofwelding heads, the loaded welding heads subsequently all receivingwelding current simultaneously.
 5. A machine according to claim 4, inwhich there are three wire loaders and the three loaded welding headseach receive one phase from a 3-phase current source.